The prior art, such as, for example, unexamined Japanese Patent Publication HEI 3-65943 describes a stereo-graphic display apparatus. The apparatus has a liquid crystal display panel and a projection lens. Images displayed on the liquid crystal display panel are projected by the projection lens on a screen. The screen has a diffusion plate and a lenticular plate. By the function of the lenticular plate, an observer can recognize a stereo-graphic image from the screen.
FIG. 7 shows the principle of a stereograph. A screen 1 has a diffusion plate 3 and a lenticular plate 5. An image is projected from a projection device (not shown in FIG. 7) on the diffusion plate 5. Left picture elements 7 of the projected image and right picture elements 9 of the projected image are projected on the diffusion plate 5. The left picture elements and the right picture elements are disposed alternately with each other in a horizontal direction 11 of the screen 1.
The lenticular plate 5 has a plurality of elongated strips of lenticular lenses 13 oriented along a vertical direction on the screen. The vertical direction is drawn as perpendicular to the horizontal direction 11 and the surface of the drawing page. Each lenticular lens 13 has a width 14 which is approximately equal to a length 10 of two picture elements along the horizontal direction 11.
Light from each picture elements 7, 9 of the projected image is refracted by the lenticular lens 13 and reaches the eyes 15, 17 of an observer. More particularly, the light from the left picture element 7 reaches the left eye 15 of the observer, and the light from the right picture element 9 reaches the right eye 17 of the observer. The right picture elements 7 and the left picture elements 9 contain image information with a parallax similar to that of the binocular parallax by which a person can sense stereo-graphic vision. (The image information is called a parallax information hereafter.) As a result, the observer can sense stereoscopic vision from the screen 1.
FIG. 7 shows only an ideal status about the right and the left picture elements. As described above, the projected image on the screen 1 comes from a liquid crystal display panel (not shown in FIG. 7). The liquid crystal display panel includes a black matrix region which light can not pass through. The black matrix separates picture elements of the liquid crystal display panel from each other. The black matrix also protects from light thin film transistors and bath-lines that drive a liquid crystal. Because of the presence of the black matrix, shadows of the black matrix are formed on the screen 1. The shadow on the screen may effect the quality of the image.
FIG. 8 shows the situation mentioned above. Shadows 8 of the black matrix are formed between the picture elements 7 and the picture elements 9 on the screen 1, since the black matrix region is disposed between each picture element of the liquid crystal display panel and the black matrix does not pass light therethrough. The lenticular lens 13 provides images 21, 22 and 23 on an imaginary plane 19. Therefore, when the observer is moving along the horizontal direction 11, he may see the shadows 21 of the black matrix in the liquid crystal display panel. As a result, the quality of the displayed image deteriorates.
One method for preventing the deterioration of the quality of the displayed image is to use a plurality of projector devices. For example, two projector devices respectively project left and right picture elements, and two picture elements from the projector devices are superimposed on a screen. Left picture elements and right picture elements are focused alternately along the horizontal direction 11. For example, as shown in FIG. 9, four picture elements in one lenticular lens 13 are used. The four picture element include a first left picture element 31L, a first right picture element 31R, a second left picture element 32L, and a second right picture element 32R. The first left picture element 31L and the second left picture element 32L are projected from a first projector device (not shown in FIG. 9). The first right picture element 31R and the second right picture element 32R are projected from a second projector device (not shown in FIG. 9). The method of using four picture elements is called the multiple-eye method or four eye-method. This method is preferable to enlarge a region in which an observer can sense a stereo-graphic view as compared to a two eye method, such as for example, shown in FIG. 7.
As shown in FIG. 9, since the width of the black matrix, on the diffusion plate 3 along the horizontal direction 11, is narrower than the width of each picture element, adjacent picture elements overlap with each other to form superimposed portions 33 when the four picture elements are projected alternately by the two projector devices. These superimposed portions 33 deteriorate the quality of stereo-graphic image, because the image obtained by the lenticular lens contains redundant information generated by interference between adjacent picture elements.
The degree of the above image deterioration problem depends on the ratio between the width of the black matrix and the width of aperture part, namely, the picture element of the liquid crystal display panel. The image quality may be improved by optimizing the ratio. However, the ratio should be adjusted depending on the diffusion characteristics of the diffusion plate 3, which vary substantially from one diffusion plate to another. Therefore, it is not very practical and economical to optimize the ratio in the manufacturing process. In other words, if the diffusion characteristics of a diffusion plate differ, it is necessary to prepare a different liquid crystal display panel which has a different ratio between the width of the black matrix and the width of the aperture part.
The problem of the deteriorated image quality is not limited to a stereo-graphic video projector having a plurality of projector devices. An ordinary video projector having a plurality of projector devices may suffer the same problem.